Transition metal orotic acid complexes

Complexes of orotic acid with transition metals (Cu²⁺, Mn²⁺, VO²⁺, Zn²⁺, Hg²⁺, Cd²⁺, Fe³⁺, Cr³⁺, and Ag⁺) have been prepared and characterized by elemental, conductivity, magnetic measurements, i.r., n.m.r. and diffuse reflectance spectra. The ligand, in its monoanion form, coordinates through the carboxylic group to the metal. The Co²⁺ complex was also isolated under alkaline conditions and studied.     

Electronic structure of transition metal dicarbollide complexes

This paper reports on the results of our electronic structure study of bisdicarbollide complexes of transition metals Fe, Co, Ni, and Cu (36 compounds) by X-ray photoelectron and X-ray emission spectroscopy. Translated fromZhurnal Struktumoi Khimii, Vol. 40, No. 2, pp. 358–371, March–April, 1999.     

The thermal properties of some metal complexes of diethyldithiocarbamic acid

The cobalt(II), cadmium(II), copper(II), mercury(II), nickel(II) and zinc(II) complexes of diethyldithiocarbamic acid were prepared and investigated by TG, DSC thin-layer chromatography and gas-liquid chromatography. Heats of fusion were determined.Permission to publish this paper has been given by the Government Chemist, Ministry of Technology.     

Synthesis, spectroscopic and thermal characterization of some transition metal complexes of folic acid

Compounds having general formula: [M(FO)(Cl)(x)(H(2)O)(y)].zH(2)O, where (M=Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II), FO=folate anion, x=2 or 4, y=2 or 4 and z=0, 1, 2, 3, 5 or 15) were prepared. The obtained compounds were characterized by elemental analysis, infrared as well as electronic spectra, thermogravimetric analysis and the conductivity measurements. The results suggested that all folate complexes were formed by 2:1 molar ratio (metal:folic acid) as a bidentate through both of the two carboxylic groups. The molar conductance measurements proved that the folate complexes are electrolytes. The kinetic thermodynamic parameters such as: E*, DeltaH*, DeltaS* and DeltaG* were estimated from the DTG curves. The antibacterial evaluation of the folic acid and their complexes was also done against some Gram positive/negative bacteria as well as fungi.     

The thermal properties of some metal complexes of diethyldithiocarbamic acid new volatile metal chelates

The cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and mercury(II) complexes of diethyldithiocarbamic acid were prepared and their thermal properties determined by TG, DTA, and high temperature reflectance spectroscopy. It was found that the copper(II), nickel(II), and zinc(II) chelates were completely volatile and thus represent a new class of volatile metal chelates. Vapor pressure measurements were made on four of the metal complexes; heats of vaporization ranged from 9.3±0.2 kcal/mole for Na[Co(DDC)₃] to 24.2±0.6 kcal/mole for Zn(DDC)₂.

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Zusammenfassung Es wurden die Komplexe von Kobalt(II), Nickel(II), Kupfer(II), Zink(II), Cadmium(II), Silber(I) und Quecksilber(II) mit Diäthyldithiokarbaminsäure hergestellt und ihre thermischen Eigenschaften durch Thermogravimetrie, Differentialthermoanalyse und Hochtemperatur Reflexions Spektroskopie untersucht. Man fand, daß die Kupfer(II)-, Nickel(II)- und Zink(II)-Komplexe vollständig verflüchtigen. Sie stellen eine neue Sorte flüchtiger Metallchelate dar. Dampfdruckmessungen wurden an vier der Komplexe unternommen. Die Verdampfungswärmen liegen zwischen den Werten von 9.3±0.2 Kcal/Mol für Na[Co(DDC)₃] bis 24.2±0.6 Kcal/Mol für Zn(DDC)₂.

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Résumé On a préparé les complexes de cobalt(II), nickel(II), cuivre(II), zinc(II), cadrnium(II), argent(I) et mercure(II) avec l'acide diéthyle-dithiocarbaminique et étudié leurs propriétés thermiques par TG, ATD et spectroscopie de reflexion à haute température. On a trouvé que les complexes de cuivre(II), nickel(II) et zinc(II) volatilisent parfaitement; ils représentent une nouvelle sorte de chélates métalliques volatiles. On a fait des mesures de pression de vapeur sur quatre de ces complexes. Les valeurs des chaleurs de vaporisation s'étalent de 9.3±0.2 kcal/mole pour Na[Co(DDC)₃] jusqu'à 24.2±0.6 kcal/mole pour Zn(DDC)₂.

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[II], [II], [II], [II], [II], [I] [II] , . , [II], [II] — . ë -; 9,3±0,2 / Na[Co(DDC)₃] 24,2±0,6 / Zn[DDC]₂.

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The partial support of this work by the U. S. Air Force, Air Force Office of Scientific Research, through Grant No. AF-AFOSR 69-1620, is gratefully acknowledged. One of us (G. D'A.) wishes to thank the National Research Council of Italy, Rome, Italy, for financial support.     

On some transition metal complexes having orientational properties

The orientation properties of some complexes of chromium (III) or cobalt (II) with oxygen-containing ligands are presented. The orientation obtained is mostly homeotropic. The possibility of anchoring by coordination of liquid crystal (LC) molecules to the transition metal ion within the alignment layer is discussed on the basis of spectroscopic arguments.     

Electronic structure and properties of transition metal-benzene complexes.

A comprehensive theoretical study of the geometries, energetics, and electronic structure of neutral and charged 3d transition metal atoms (M) interacting with benzene molecules (Bz) is carried out using density functional theory and generalized gradient approximation for the exchange-correlation potential. The variation of the metal-benzene distances, dissociation energies, ionization potentials, electron affinities, and spin multiplicities across the 3d series in MBz complexes differs qualitatively from those in M(Bz)(2). For example, the stability of Cr(Bz)(2) is enhanced over that of CrBz by almost a factor of 30. On the other hand, the magnetic moment of Cr(Bz)(2) is completely quenched although CrBz has the highest magnetic moment, namely 6 mu(B), in the 3d metal-benzene series. In multidecker complexes involving V(2)(Bz)(3) and Fe(2)(Bz)(3), the metal atoms are found to couple antiferromagnetically. In addition, their dissociation energies and ionization potentials are reduced from those in corresponding M(Bz)(2) complexes. All of these results agree well with available experimental data and demonstrate the important role the organic support can play on the properties of metal atoms/clusters.     

Preparation, characterization and thermal studies of some transition metal ternary complexes

Ternary complexes of Co(II), Ni(II), Cu(II) and Zn(II) with nitrilotriacetic acid as a primary ligand and glycine as secondary ligand were prepared in slightly acid medium. Their molecular masses were determined by acid-base titration against standard potassium hydroxide solution. Their molecular structures were found to be [M (HNTA)(glyH)(2H₂O)]. Thermogravimetric analysis confirmed this structure and that the water present is coordinated to the central metal atom. UV-Vis spectra showed that the complexes have octahedral symmetry. IR spectra suggested the presence of intermolecular hydrogen bonding. This phenomenon was supported by mass spectra. The ionization constants of these complexes, as diprotic acids, were determined.     

Electronic structure and transport properties of early transition metal tripledeckers

The electronic structure and transport properties of the Cp(2)BzM(2) (M = Sc, Ti, and V) tripledeckers are studied by spin polarized density functional theory and nonequilibrium Green's function method considering high-spin and low-spin states. Total energy calculations show that the sandwich structured Cp(2)BzSc(2) exists in a singlet state with no local magnetic moment on the Sc atoms. Cp(2)BzTi(2) in triplet state exists as a distorted tripledecker and is more stable than singlet and quintet states. Cp(2)BzV(2) stabilizes in the quintet state with a spin density of 2.4 on each vanadium atom. Hund's coupling plays a vital role in stabilizing the higher multiplets in case of titanium and vanadium clusters. In bigger clusters like Cp(3)Bz(2)M(4), Sc multidecker has one unpaired spin, Ti multidecker has five unpaired spins, and V multidecker has seven unpaired spins in total. Spin polarized electronic transport is found for all states of vanadium tripledecker and one state of the titanium tripledecker when connected to a gold two probe junction. Moderate to high-spin filter efficiencies are calculated for these states. Cp(2)BzSc(2) shows spin-independent electronic transport for all electronic states when introduced in the gold two probe junction. Current versus voltage curves are reported for selected clusters in the two probe setup.     

Coordination and structure of some transition metal piperidinium pentamethylene dithiocarbamate complexes

Summary Cobalt(II), nickel(ll), and copper(II) complexes of piperidinum pentamethylene dithiocarbamate (pipmdte) have been prepared and studied by spectral (i.r. and absorption) and magnetic methods. The M(pipmdte)CI complexes are probably four coordinate and square planar, the tridentate ligand being coordinated via the two thiocarbamate sulphur atoms and the nitrogen atom of the piperidinium group.     

Kinetics of thermal dehydration of some bis-salicylato-diaquo complexes of transition metal ions

The kinetics of thermal dehydration of bis-salicylato-diaquo complexes of VO(II), Cu(II), Ni(II), Co(II), Fe(II), Mn(II) and Zn(II) were studied. The activation energies and other kinetic parameters were evaluated. The observed kinetic parameters indicate first-order reactions. The activation energy of the thermal dehydration decreases in the sequence VO(II) > Cu(II) > Zn(II) > Co(II) > Ni(II) > Fe(II) > Mn(II), which is also the sequence for the difference in carboxyl group IR frequency.

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Zusammenfassung Die Kinetik der thermischen Dehydratisierung von Bis-salicylato-diaquo-Komplexen von VO(II), Cu(II), Ni(II), Co(II), Fe(II), Mn(II) und Zn(II) wurden untersucht. Aktivierungsenergien und andere kinetische Parameter wurden bestimmt. Die beobachteten kinetischen Parameter weisen auf Reaktionen erster Ordnung hin. Die Aktivierungsenergie der thermischen Dehydratisierung nimmt in der Reihenfolge VO(II) > Cu(II) > Zn(II) > Co(II) > Ni(II) > > Fe(II) > Mn(II) ab. In der gleichen Reihenfolge ändert sich auch die IR-Frequenz der Carbonylgruppe.

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-- , , , , , . , . VO(II) > Cu(II) > Zn(II) > Co(II) > Ni(II) > Fe(II) > Mn(II). .

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The authors express their sincere thanks to the late Dr. M. D. Karkhanawala (then Head, Chemistry Division, BARE, India), for providing the facilities for TG and DTA, and also to the UGC (India) for research fellowships to the authors (BDH and SMA).     

Synthesis, spectral and thermal properties of some transition metal(II) complexes with a novel ligand derived from thiobarbituric acid

Four novel metal(II) complexes, Ni(L)₂, Co(L)₂, Cu(L)₂, and Zn(L)₂ (L = 5-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)hydrazono)-1,3-diethyl-2-thioxo-dihydropyrimidine-4,6(1H,5H)-dione), were synthesized using the procedure of diazotization, coupling and metallization. Their structures were identified by elemental analyses, ¹H NMR, ESI-MS and FT-IR spectra. The effect of different central metal(II) ions on absorption bands of the metal(II) complexes was researched. The thermal properties of the metal(II) complexes were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). Furthermore, the thermodynamic parameters, such as activation energy (E*), enthalpy (?H*), entropy (?S*) and free energy of the decomposition (?G*) are calculated from the TG curves applying Coats–Redfern method. The results show that the metal(II) complexes have suitable electronic absorption spectra with blue-violet light absorption at about 350–450 nm, high thermal stability with sharp thermal decomposition thresholds.     

Synthesis,characterization and thermal study of some tetradentate Schiff base transition metal complexes

Several mononuclear Co(II), Ni(II), Cu(II), and Fe(II) complexes of tetradentate salpren-type diimine, obtained from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 1,3-diaminopropane have been prepared and characterized by analytical, spectroscopic (FT-IR, UV–VIS) techniques, magnetic susceptibility measurements and thermogravimetric analyses (TG). The thermodynamic and thermal properties of complexes have been investigated. For further characterization Direct Insertion Probe-Mass Spectrometry (DIP-MS) was used and the fragmentation pattern and also stability of the ions were evaluated. The characterization of the end products of the decomposition was achieved by X-ray diffraction. The thermal stabilities of metal complexes of N,N′-bis(3,5-di-t-butylsalicylidene)-1,3-propanediamine ligand (L) were found as Ni(II) > Cu(II) > Co(II) > Fe(II).     

Syntheses and thermal properties of some complexes with 2-mercaptonicotinic acid

The biological activity of a kind of hetero-bimetallic Schiff-base complex was studied using Escherichia coli (E. coli) cell as the target. By microcalorimetry, the difference of anti-bacterial activity between the binuclear Schiff-base and the ligand was determined and analyzed. To analyze the inhibition of the bacterial growth internally, the E. coli cells grown in the presence of hetero-bimetallic Schiff-base complex were observed by scanning electron microscopy. The images in high resolution revealed the damage of outer cell membrane caused the inhibitory effect on E. coli. Inductively coupled plasma-mass spectrometry results proved the absorption of the complex by cells, which confirmed the interaction between the Schiff-base and biological macromolecule.     

Electronic structures of multi-decker transition metal sandwich complexes

The electronic structures of multi-decker transition metal sandwich complexes are discussed according to the structure rules for transition metal heterocarboranes. A series of skeletons of the structures Fe₂C₅(D_5h), Ni₂C₅(D_5h), V₂C₆(D_6h), Co₂C₆(D_6h), and Fe₂C₄(D_4h) are calculated using the EHMO method. The calculated results show that the number of valence bonding orbitals (VBO) can vary as the distance between the metal atoms in the metalocenes is increased. This fact can be used to explain the number of valence electrons (VE) in triple-decker sandwich complexes. The conclusions are proved and discussed through a theoretical analysis of the electronic structures of such complexes and through EHMO calculations for actual compounds containing 29–34 valence electrons.     

Electronic structure and optical spectra of transition metal complexes by the effective Hamiltonian method

Summary A semiempirical effective Hamiltonian treatment is proposed for transition metal complexes, taking into accountd-electron correlations, weak covalency of the metal-ligand bonds and the electronic structure of the ligand sphere. The technique uses the variation wave function which differs from the usual Hartree-Fock antisymmetrized product of molecular orbitals extended over the whole complex. The scheme is implemented and parameters describing the metal-ligand interactions are adjusted to reproduced-d-excitation spectra of a number of octahedral MF ₆ ^4– (M=Mn, Fe, Co, Ni) anions, Mn(FH) ₆ ²⁺ cation, CoCl ₆ ^4– anion, and a tetrahedral CoCl ₄ ^2– anion. The values of the parameters are reasonable, thus confirming the validity of the proposed scheme.     

Preparation and thermal behaviour of divalent transition metal complexes of pyromellitic acid with hydrazine

Hydrazine forms two different types of complexes with divalent metal ions and pyromellitic acid (H₄pml) in aqueous medium: (i) hydrazinium complexes of formulae, (N₂H₅)₂M(pml)·xH₂O, where x = 3 for M=Ni and x = 4 for M=Co or Zn, and (N₂H₅)₂Mn(H₂pml)₂, at pH 4.5, (ii) neutral hydrazine complexes with formulae, M₂(pml)(N₂H₄) _n ·xH₂O where M=Co or Ni when n = 4 and x = 5 or 4 and M=Zn or Cd when n = 2, and x = 4 or 3 at pH 7, and M(H₂pml)(N₂H₄)·xH₂O where x = 4; M=Cu and x = 0; M=Hg, at pH 3, 7.5, respectively. All the complexes are insoluble in water, alcohol and ether. The N–N stretching frequency (990–1,007 cm⁻¹ for coordinated hydrazinium ion and 956–985 cm⁻¹ for bridged neutral hydrazine) indicates the nature of hydrazine present in the complexes. Simultaneously TG-DTA analysis indicates that hydrazinium complexes undergo dehydration and dehydrazination in a single step endothermally in the range of 289–300 °C whereas neutral hydrazine complexes undergo endothermic dehydration (~100 °C) followed by exothermic dehydrazination in the temperature range, 253–332 °C. The anhydrous metal carboxylates further decompose exothermally to leave the respective metal oxides or metal carbonates except zinc, which gives its oxalate as the end product. X-ray powder patterns indicate that even the complexes with the same formulation possess no isomorphism.     

Properties of some tetraphenylboronates of transition metal complexes

Summary Solid tetraphenylboronates of some cations,e.g. [Fe(1,10 phen)₃]³⁺ , [Co(NH₃)₆]³⁺, with E° values -0.26V are unstable, either thermally or photo chemically, or both. Products of such redox reactions are identified. The contrasting situation with more reducing cations,e.g. [Cr(en)₃ ]³⁺, is described.On leave from Paisley College of Technology, Renfrewshire, Scotland, U.K.     

Molecular orbital studies of some transition metal complexes

A set of molecular orbital calculations based on a particular semi-empirical method, has been undertaken on a homologue series of bis(-2-methylallyl)transition metal (Ni, Co, Fe, Cr) complexes (abbreviated as ML₂). Arguments are found for predicting the stability of the NiL₂ system, which is the only one that could be synthetized.

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Zusammenfassung Eine Reihe von semiempirischen MO-Rechnungen wurde für die homologe Reihe von bis(-2-methylallyl) Metallkomplexen (Ni, Co, Fe, Cr) durchgeführt. Gründe für die Stabilität der Ni-Verbindung, die als einzige synthetisiert wurde, werden angeführt.

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Résumé Un ensemble de calculs par une méthode semi-empirique particulière d'orbitales moléculaires a été effectué sur une série homologue de complexes bis (-2-méthylallyl)-métal de transition (Ni, Co, Fe, Cr): ML₂.Certains arguments sont trouvés en faveur de la stabilité du système NiL₂, le seul à avoir été synthétisé.